From a127a332ac940b05eb0039fbcdd5434358dfb9a7 Mon Sep 17 00:00:00 2001
From: Alex Shinn <alexshinn@gmail.com>
Date: Sun, 9 Jan 2022 21:29:00 +0900
Subject: [PATCH] use 0 (configurable) for the C++ size of flexible arrays
 (fixes #808)

---
 include/chibi/features.h | 9 +++++++++
 include/chibi/sexp.h     | 4 ++--
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/include/chibi/features.h b/include/chibi/features.h
index a4c22954..e9e85d96 100644
--- a/include/chibi/features.h
+++ b/include/chibi/features.h
@@ -324,6 +324,15 @@
 #define SEXP_MAX_ANALYZE_DEPTH 8192
 #endif
 
+/* The size of flexible arrays (empty arrays at the end of a struct */
+/* representing the trailing data), when compiled with C++.  Technically */
+/* 0 is an illegal value here, and the C++ idiom is to use 1, but this */
+/* breaks compatibility with C when computing the size of structs, and */
+/* in practice all of the major C++ compilers support 0. */
+#ifndef SEXP_FLEXIBLE_ARRAY_SIZE
+#define SEXP_FLEXIBLE_ARRAY_SIZE 0
+#endif
+
 /************************************************************************/
 /*         DEFAULTS - DO NOT MODIFY ANYTHING BELOW THIS LINE            */
 /************************************************************************/
diff --git a/include/chibi/sexp.h b/include/chibi/sexp.h
index f82d588d..5edef840 100644
--- a/include/chibi/sexp.h
+++ b/include/chibi/sexp.h
@@ -1,5 +1,5 @@
 /*  sexp.h -- header for sexp library                         */
-/*  Copyright (c) 2009-2015 Alex Shinn.  All rights reserved. */
+/*  Copyright (c) 2009-2022 Alex Shinn.  All rights reserved. */
 /*  BSD-style license: http://synthcode.com/license.txt       */
 
 #ifndef SEXP_H
@@ -7,7 +7,7 @@
 
 #ifdef __cplusplus
 extern "C" {
-#define SEXP_FLEXIBLE_ARRAY [1]
+#define SEXP_FLEXIBLE_ARRAY [SEXP_FLEXIBLE_ARRAY_SIZE]
 #else
 #define SEXP_FLEXIBLE_ARRAY []
 #endif